1. Field of the Invention
The present invention relates to a laser light reflection method and a laser light reflection device for an aircraft-installed laser apparatus, and more particularly to a laser light reflection method and a laser light reflection device for an aircraft-installed laser apparatus with which, when a function check is performed on the laser apparatus by emitting laser light from a parked aircraft to a body exterior, a reflection mirror can be disposed in direct opposition to a laser emission direction, an elevation of a reflection direction of laser light reflected by the reflection mirror relative to a horizontal direction can be measured accurately and easily, and actual emitted laser light can be reflected in a desired direction safely and efficiently.
2. Description of the Related Art
In recent years, air turbulence has gained attention as a principle cause of aircraft accidents, and therefore research and development is being undertaken into a Doppler LIDAR using laser light as an apparatus installed in an aircraft to detect air turbulence in advance (see H. Inokuchi, H. Tanaka, and T. Ando, “Development of an Onboard Doppler LIDAR for Flight Safety,” Journal of Aircraft, Vol. 46, No. 4, pp. 1411-1415, July-August 2009, for example). Note that a LIDAR is a detection method employing light, and is an abbreviation for “Light Detection and Ranging”. It is also referred to as Doppler LIDAR since a wind speed is measured by receiving scattered laser light generated when an emitted light beam is scattered by minute aerosols floating in the atmosphere, and by measuring frequency variation (wavelength variation) therein due to the Doppler Effect. A LIDAR can measure local wind speeds up to a distance of approximately several tens of km simultaneously by dividing a distance in a laser emission axis direction into intervals of approximately 150 m. A wavelength in a near infrared region, which exhibits little attenuation over long distances, is used mainly as the laser light, and the safety of the laser light is high. However, taking into consideration the possibility of unanticipated convergence at great distances due to the fact that little attenuation occurs over long distances, the laser light must be emitted after confirming that no personnel are present in the laser emission direction.
When a function test is implemented on a Doppler LIDAR on the ground, the function test can be performed on a single device unit by setting a direction of a laser emission unit freely while confirming safety. However, when the device is installed in an aircraft, the laser emission unit is fixed, and when laser light is emitted from the fixed laser emission unit, the laser light may be emitted in a direction in which safety cannot be confirmed, such as in the direction of a ground surface or a building. For example, in a flight test performed on a LIDAR by the Japan Aerospace Exploration Agency (to be referred to hereafter as “JAXA”), the laser emission unit is attached at a downward orientation of 2.5 degrees relative to a body axis so that during flight, the laser light is emitted in a substantially horizontal direction. Actual measurements are taken in advance so that the body axis is oriented 1 degree downward from the horizontal direction during parking, and therefore, during parking, the laser light is emitted at a downward orientation of 3.5 degrees relative to the horizontal direction. Hence, when the laser light is emitted after the LIDAR is installed in the body, the laser light impinges on the ground surface, and in this condition, a function check cannot be performed on the LIDAR.
In response to this problem, the inventor of the present application attempted to modify the emission direction of the laser light by fixing a reflection mirror to a camera platform on a tripod.
Note that a technique of fixing a reflection mirror to a camera platform is widely known, and a known invention (see Japanese Patent Application Publication No. 2004-288565, for example) pertains to a sunlight irradiation device configured such that sunlight is reflected by a reflection mirror attached to a camera platform and emitted onto a shady portion, for example.
However, it was found that in actuality, when a laser light emission direction is reflected using a reflection mirror fixed to a camera platform on a tripod, the following three problems occur.
As a first problem, invisible infrared rays are used as the laser light, and therefore the reflection mirror cannot be disposed correctly in a center of the laser emission direction.
As a second problem, the direction in which the laser light is reflected by the reflection mirror is not known, and therefore safety cannot be confirmed in relation to the laser reflection direction.
As a third problem, an aerosol density varies greatly according to altitude, and therefore an elevation value of the laser reflection direction relative to the horizontal direction is required to calculate the approximate altitude of the wind speed to be measured. However, since the laser reflection direction is not known, the elevation value of the laser reflection direction relative to the horizontal direction cannot be calculated.